GB1148324A - Improvements in regulating systems for pressure medium - Google Patents

Abstract

1,148,324. Fluid-pressure servomotor systems. ROBERT BOSCH G.m.b.H. June 17, 1966 [June 19, 1965], No.27172/66. Heading G3P. A control system for a variable displacement pump 10 maintains the product of the delivery and output pressure of the pump constant. As shown, a piston 14, 15 carries a spool 21 bearing on a balance lever 27 pivoted at 28 and supported by an adjustable spring 29. The piston also carries a web 31 which provides a pivot 32 for a right triangular member 33, the latter also engaging a fixed knife-edge 34. A plunger 36 abuts member 33 and passes through a sleeve 39 slidable in a bore 38. The point of engagement 35 of plunger 36 with member 33, knife-edge 34 and pivot 28 all lie on a common straight line. The output line 65 of the pump includes a restriction 66 the pressures across which are communicated to the control system via lines 64, 67. Downstream, i.e. outlet, pressure acts on the top on spool 21 via lines 67, 62, chamber 13' and line 22, thus the spool exerts a force F 2 on the lever 27 proportional to the outlet pressure. The moment arm h of this force is proportional to the square root of the distance m since the distance n remains constant. The distance m is proportional to the pressure across restriction 66, i.e. proportional to the square of the flow-rate, thus the distance h is proportional to the flow-rate. The moment F 2 , h is thus proportional to the required product and the latter is constant when lever 27 is in equilibrium. If the downstream pressure rises, e.g. due to speed increase of motor 11 or falling demand, spool 21 moves downwardly to vent chamber 13" and thereby allow piston 14, 15 to move to the right until spool 21 is returned to its neutral position by contact with the lever 27. The rocking of member 33 allows plunger 36 to fall under the action of pressure in chamber 37. Upstream pressure now acts via line 64, chamber 40, the gap between control edges 47', 48" on sleeve 39 and plunger 36 respectively, passages 49, 50 in plunger 36 and lines 53, 59 on servopiston 61 to cause the latter to reduce pump output by tilting the pump casing. The increased downstream pressure non acts via line 63 and chamber 41 on sleeve 39 to move the latter downwardly to lap control edges 47', 48". The system is returned to equilibrium when the moment exerted on lever 27 by the product of the lower flow-rate and the higher outlet pressure balances the moment exerted by spring 29. When the outlet pressure reaches a predetermined value it lifts a spool 54 and acts via line 59 on the servopiston 61 to move the pump to its zero-delivery position. Springs 29, 56 could be replaced by hydraulic loads. If desired, the servopiston could alternatively actuate a valve in line 65. In the embodiment of Fig.2, (not shown), the pressure difference acts on the lever (27) and the moment arm is proportional to the square of the outlet pressure; this system thus acts to maintain N<SP>2</SP> = P<SP>2</SP>, Q<SP>2</SP> = const, P being the pressure and Q the delivery.